Ion Modulated Electroactivity in Thin Film Metallopolymers

Abstract : Electroactivity in thin-film redox polymers derived from Fe(2, 2'bipyridine)3(3+/2+) and Fe(phenanthroline)3(3+/2+) can be tremendously modulated by replacing conventional counter ions (such as perchlorate) with alkylsulfonates (CH3(CH2) nSO3, n=0-11). With large n species, the amount of charge passed during metal oxidation decreases (reversibly) by nearly an order of magnitude, while the rate of charge flow (as measured transiently by chronocoulometry) similarly decreases, again reversibly. Redox thermodynamic effects (systematic shifts in film-based formal potentials) are also seen. The unusual coupling of redox and ionic conductivity processes uncovered here appears to be related to: (1) the large free-volume demands of the alkylsulfonates, and (2) fundamental limitations on the ability of the metallopolymer to meet those demands.